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Blue is purple

09-04-2007, 07:01 AM

Hi All

We are experiencing a problem with supplied CMYK scans from a customer. The scans are of paintings and we believe they have been converted to CMYK using a Euroscale V2 profile. A few of the scans contain a blue colour, for example as part of a dress. They look blue on a our calibrated monitors but they proof on our Dupont Largo as something more akin to purple. We have two standards on our Largo, EuroStandard and Gracol. These were only recalibrated last week and on an IT/8 target with 1617 swatches we are getting an average Delta E of about 1.1, so we know they are pretty accurate.

The colour break on the blue is in the range 100/90/30/40 <-> 100/85/36/21 which to me is somewhere in the middle between blue and purple., but it definitely appears blue on screen. The problem is the customer sees the blue and this is what they want. I'm finding it difficult to convince them that our proofing is accurate and that the problem is the way that this colour is being shown on their (and our monitors). We have re-calibrated our monitors and they reflect the purple better but we still cannot match it. I need have an understanding of why it isn't being represented properly and also what I can get the customer to do so it shows on his monitor better.

Comment

The blue going to purple has something to do with the program that made the CMYK profile. The mapping of out-of gamut colors to CMYK is all included in the profile. I would:
1. Try to get the RGB (with RGB ICC profile embedded) from the customer.
2. Try using the official GRACoL2006_Coated1v2 ICC profile and converting from RGB to CMYK using either Relative Colorimetric Intent or Perceptual Intent.

Don

Comment

Are the files tagged with a profile? What are your Color Management policies in Photoshop when opening a file? Do you preserve the embedded profile? If so, try assigning another CMYK profile (your usual CMYK working space) and see if that blue onscreen comes closer to what you are getting on proof. If so, you will need to open the image preserving supplied profile and do a CMYK to CMYK profile conversion to your usual working CMYK space.
Hope this helps.

Better train people and risk they leave - than do nothing and risk they stay.

Comment

As far as we know they were scanned RGB and converted to CMYK before the got to us using a Euroscale V2 profile. There are no profiles currently attached to the files.

I know that these colour breaks are defintely heading towards purple but I can't explain why it looks so blue on screen. Not matter what Colour Settings we use in Photoshop we can't get the scan to appear purple on screen, it always remains blue (ish). It's not a calibration issue on the monitor as it's been calibrated/profiled with an Eye-one and Monaco, so it's just a preview issue but I'm a bit lost as to what to tell the customer. The see blue, they expect blue, they get purple.

Comment

Hi,
Definitely the costs have to to be reconsidered using spot additional colors but at the end we are talking about what CMYK can do and what the customer wants. The replication of paintings with offset printing is always a challenge and requires compromises on both sides. At the end is the question: How close the colors can or should match.
Buying additional software only for this job might be also not such good advise but having this kind of features makes you different from your competitors and might open new doors.
Gerhard

Comment

OK. If you have CMYK, do you have an output ICC profile (characterization of your press/paper/ink combo) (Note: You can use Euroscale profile if that is what was used for separation AND your press printing conforms to that. If not, you need to use a profile that matches what your press prints and use that for separation and soft and hard proofs)? And if you do have a profile that matches your press printing, are you soft-proofing correctly? To soft-proof correctly:
1. Open CMYK in PhotoShop
2. Click View menu > Proof Setup
3. Under Proof Conditions, choose your press/paper/ink profile for the press/paper/ink combo you will be printing on (could use official GRACoL2006_Coated1v2 for U.S. or ISOcoatedv2 for Europe if your printing conforms to it).
4. Check Preserve CMYK Numbers
5. Under Display Options (On-Screen), check both 'Simulate Paper Color' and 'Simulate Black Ink'

Now does the Blue still look blue or purple? If purple, you'll either need to convert from RGB to CMYK profile that matches your press printing on that paper type (I've discussed #1 paper here, and hope that the program that made your profile keeps blues from going purple), or you'll need to do color correction by taking down the magenta.

Note: If soft-proofing RGB, under Rendering Intent, choose a combination of rendering intents (not using Absolute Colorimetric or you will get dots in your previously white background) and black point compensation, and whichever one looks best when soft-proofing, use the same combination to actually convert the RGB to CMYK.

Comment

Although your *average* delta across the chart is about 1.1, what is the *maximum* delta reading?

We recently had a similar problem with proofs to press - the proof was an excellent match to press apart from one patch of solid colour - we checked our proofs and we recorded an average delta of .96, however the maximum delta was about 3.7.

When we looked at the patches with the high delta value, some were in the same sort of ballpark as the 'problem' colour. Therefore we attributed the colour match problem to this.